Whether you did this on purpose or by accident, you suddenly find yourself in possession of a fish with a the nick name “tank buster”. Congratulations you own a monster. Is your tank big enough? Can your floor support a tank that is big enough? Can you afford a tank that is big enough?

That “cute” little pacu grows into one of the true tank busters of the hobby.

    1. Some examples of commonly attained fish that may grow to be a LOT bigger than you were planning:
      • Columbian Shark (A schooling fish that gets to be at least 12 inches)
      • Tinfoil barbs (schooling fish that gets to be 14-16 inches)
      • Common goldfish (18-24 inches)
      • Common pleco (some species easily get to 24 inches)
      • Clown Knife fish (3 feet long)
      • Iridescent shark (a schooling fish that grows to be 3-4 feet long)
      • Pacu (smaller species get to be 3 feet long, larger species get to be 4 feet long, schooling)
      • Tiger shovelnose Catfish (4 feet long)
      • Arowana (4 feet long)
      • Red-tail cat fish (5 feet long)
      • Alligator gar (7-8 feet long)
      • Arapaima (12-14 feet long)

While there are many other fish in the pet industry that get to be huge, these are some of the real common ones. I have included a few fish that are only 12-16 inches long because they are schooling fish. While a single fish of 12″ long might not seem like a monster, when you have 6 or more of them together to make a group that the fish are comfortable in, you now have the equivalent of a monster.

Most fish grow at rate that allows them to reach 70-80% of their maximum body size in the first 20-30% of their life time. Meaning that your red-tail cat will easily grow more than an inch a month in its first year of life! A common misconception is that these fish can be housed in small tanks when they are small and don’t need to be moved until they get large. In order for the fish to grow properly, the tank it is in should at all times be at LEAST four times as long as the fish and at LEAST 1.5 times wider than the fish is long. Tanks should also be a LEAST 2x the height of the fish. This is particularly important for taller fish such as knifes, pacu and tin foil barbs. An example: your pacu is now 18″ long, its tank should be at minimum 6′ long by 27″ wide by 24″ deep. That sized tank will not suit your pacu for life, but will house it at its current size. When it grows the tank will need to be larger. FYI that tank will hold more than 200 gallons of water and weigh more than a ton.

Img d d d

A large Redtail catfish, they will go great in your 20 gallon won’t they?

Ok, so how does one realistically house a fish that needs 300, 500 or even 1500 gallons of water to live a healthy life?

Stock tanks: The largest stock tanks that can be purchased are about 300 gallons. Rubbermaid makes one that sells for about $300. With an oval shape, they are solid and sturdy. It is hard to view the fish, but for a few hundred dollars you have your fish safely into a 300 gallon enclosure that can be easily topped with a screen door or fishing net to keep the jumpers in their tank.

Indoor Ponds: Pond liners can be purchased in almost any size and supported in any shape desired with cinder blocks, wooden frames or even used to line a hole dug into the back yard. This option is amazingly versatile as it allows you a tank that can grow with your fish. Buying a large pond liner the first time can save the difficulties (and potential failure) of installing a seam later. In very rough numbers, these style enclosures can be built for about $1 a gallon giving you the potential for a 500 gallon tank for only $500. The shape can be as unique as the space you have to put the tank into. The obvious down sides are the inability to view your fish from any angle but the top and some complications associated with filtering.

Swimming pools: The cheapest HUGE tank you can get is a 640 gallon swimming pool made by Intex. The “Easy Set Inflatable pool” is 30″ deep and 8′ in diameter. Its major flaw is that the walls are held up by an inflatable ring that is easily punctured by things like your pet cat; or simply pushed down below the surface of the water by a child, dog or even you as you walk past or step into the pool. While I have never heard of a side wall getting punctured by a fish’s spine or tooth, I wouldn’t rule it out. I would recommend this pool as a temporary shelter to hold large fish while one tank is taken down and a second (larger one) is assembled in its place. These pools can be purchased for about $80 and come with a surprisingly good pump. A simple fishing net can be placed across the top to prevent fish from jumping out. They make a great short term solution to your long term problem.

Also made by Intex are “Frame pools” that start at 10 feet in diameter and 30″ deep. These pools hold about 1100 gallons of water and cost less than $150. Because of their frames, they are MUCH sturdier than the inflatable ones and come with the same sturdy little pump the inflatable pools come with. They offer a lot of water for very little investment if you have the space to give a 10′ pool. If using a swimming pool as a fish tank there is no realistic limit to the size you can attain. The two smallest are explained here but sizes of 10-50K gallons are readily available.

Aquaculture tanks: There are many brands sizes and shapes of aquaculture tank available. Most are made from fiberglass molds. An advantage to these is that there is an option of buying one with a viewing window. These come in round, square, rectangular and oval shapes and many depths. An example of cost is a 600 gallon tank with a viewing window 8’x 3′ x 2.5′ for $1300 (+ freight charges to deliver). There are multiple manufacturers and distributors of these large tanks. In my opinion they come in colors that are quite distasteful, but could easily have the interior painted to be a more appealing color and a light weight wooden box (3/8″ ply wood will do the trick) assembled around them to cover the ugly exterior. They are a good, sturdy, reliable way to house a LOT of water and still be able to see the fish from the side.

Homemade tanks: If you are handy and want to build your own tank, there is no limit to size, shape of complexity of design. Tanks can be built out of many things, the most common are plywood coated in fiberglass and sealed cement. You can design your tank to have as large or small a viewing window as you choose. Homemade tanks range in size from a few gallons to as many tens of thousands of gallons as you can imagine. It’s a lot of work, there are no guarantees that the tank won’t leak, but if successful can result in an immensely rewarding masterpiece for your home.

Traditional Glass/ acrylic tanks: This is probably the most traditional way to house fish, but at large sizes, it is also the most expensive. A 600 gallon glass tank will cost about $3000 new (+ the cost of shipping, lids, lights filters stands etc.…) Acrylic tanks are slightly more expensive. Used tanks are available at a fraction of the cost of new tanks if you can find one for sale.

Ok, so you have attained a giant container of water for your fish, what else do you need?


Img d c

The authors 450 gallon aquarium, note the hefty stand and what you can,t see is the beefed up floor joist in the basement.


A lid: Lids, a net, a screen door, a frame with lexan panels, or even a sheet of painted ply wood over the top will be needed to keep the fish from jumping out. Personally, I like the frame of lexan panels. If you use plastic composite boards (Trex is one brand name), the fame can be built so that it does not suffer problems from moisture and water. Lexan is transparent as glass, and can be cut and drilled with traditional wood working tools. Finger sized holes can make the panels much easier to pick up and can be used to feed the fish through.

Lights: Shop lights can be easily wired to a timer. An 8′ light with dual bulbs costs about $60, 4 foot fixtures are about half of that.

Heaters: On a tank over 200 gallons I would recommend only a metal heater, the glass ones are simply poor in efficiency in comparison, either stainless steel or titanium. The traditional rules of 3-5 watts per gallon don’t really apply to tanks this large as they have so much thermal mass that not as much heat is needed to keep them warm. 1-2 watts per gallon works just fine to maintain temperature under most circumstances.

Stand: Traditional, most homemade and some aquaculture tanks get placed on a stand. Be sure to have one that can take the weight of your tank. Estimate the tank to weigh at least 11lbs per gallon of water and then add a few hundred pounds just to be safe. An example: A 450 gallon glass tank made from ¾” glass weighs 875 Lbs empty. The water weight is 3825 lbs, and there is 300 lbs of rocks and gravel in the tank. Before the weight of the fish and filtration is included that is 5000Lbs! Traditional 2×4’s can be used to make headers for placement across the fronts of cupboard doors and make good material for building the stand. Do not take the job of building the stand lightly. The weight-load the stand must support is immense and needs to be considered carefully in the design. Indoor pools and ponds obviously don’t have stands. Stands allow for filtration to be stashed out of sight under the tank, and allow for gravity draining of the tank during water changes. Big tips for homemade stands: paint the inside white and install a few “under the cupboard” style lights. Its amazing how hard it is to see under there!

Filtration: Pumps and filters that turn the volume of your tank over several times an hour are not optional, and can be very costly. Hagen’s FX5 runs at a flow rate of 600GPH (with no head) and is the largest canister filter currently on the market. However even that can’t turn over a large tank often enough. A wet/dry filter can be run off of any pump you choose. Swimming pool filters such as those that come with the Intex pools do a surprisingly good job for low investment. They are a bit noisier to run than a traditional aquarium pump and are not advertised to have longevity beyond 2000 hours. (I have had one running now for 3600 flawlessly and was quite surprised to read the 2000 hour advertisement while I was writing this article.) A powerhead can be used to power a sponge filter for a little extra filtration and water turnover rate, they can also be used to run an aquaponics tray that could do amazing things towards reducing nitrates in your water as well. The heavier the stock of the tank the more filtration it will need. A lightly stocked tank should have its volume of water run through its filters at least 3-4 times an hour, heavily stocked tanks will benefit from 8-10 times an hour. I would recommend to anyone, that they use multiple forms of filtration on any size tank: large or small. A sump filter running off of a good pump, combined with a canister filter (or 2) and either an HOB (such as an Emperor 400) or a power head on a sponge filter makes a great team of filtration options that gives all the benefits that each filter style comes with.

Supporting the weight in your home. If possible put the tank on a concrete slab. I would never encourage anyone to put a tank larger than 180 gallons on a second (or higher) floor no matter how well built the home is. If the tank must go over an open space such as a basement, placing the tank across as many supports as possible is important. Meaning, place it perpendicular to your floor joists. Adding additional support beams that run the length of the tank can be done if you want your tank to run parallel to the joists. Consider putting in an extra support pole in your basement regardless.


Img ec cc

Pacus in their new home. Now that 19 inch pacu doesn’t look too big for the tank!

5/5 - (17 votes)


Please enter your comment!
Please enter your name here